Cows fed tropical leaves burp out a lot less methane

Cow burps are a large source of greenhouse gases(Credit: Nick Lavars/New Atlas)

Much like a partner might make the decision to stop cooking a loved one beans for breakfast, scientists are investigating ways to reduce the methane emissions from cows by altering their diets. The latest promising development in the area comes from scientists in Mexico, who have found that supplementing cow food with leaves of tropical trees and flowers can cause a sharp decline in their gaseous output.

Methane from cows is a big problem for the environment, as it is from other sources, because as a greenhouse gas it is 28 times more potent than carbon dioxide due to its superior radiation-trapping abilities. So with more than 90 million cows plodding around the US alone, scientists have been moved to explore ways to reduce the environmental impact of the livestock industry.

While plenty might assume that bovine backends are responsible for releasing methane, most of it comes from cow burps, around 90 percent of it, in fact. In any case, researchers have made some progress toward limiting the damage, with Australian scientists recently discovering a strain of seaweed that can reduce bovine methane emissions by 99 percent.

The latest study doesn't offer quite such game-changing numbers, but does present a new potential tool in the effort, and the results are nothing to sneeze at either. Scientists at the Autonomous University of Mexico State studied cows across four sites in Mexico that had been fed grasses mixed with leaves from leucaena trees and cosmos flowers, both native to the region.

The leaves contain tannins that kill bacteria and disrupt the fermentation process that the animals use to break down their food (and make methane), without interfering with their digestion. The addition of the cosmo flower leaves were found to reduce methane emissions by 26 precent, while the leucaena leaves cut them by 36 percent, compared to a regular grass diet. What's more, the scientists found that the leucaena leaves actually served to improve the cows' milk production.

Although the plants used in this pilot project were local to tropics, the researchers say plants containing tannins in other regions could be identified and used to soften the blow of the bovine belching, putting a dent in global greenhouse gas emissions in the process. They presented their work at a meeting of the American Geophysical Union last month.